Today's complex products often contain multiple devices such as processors and microcontrollers to drive the products. As the number of devices increased and the size of the product decreased, printed wire boards were used to improve device density. Printed wire boards (PWB) (alternatively referred to as printed circuit boards (PCB)) host a number of semiconductor devices connected via circuits or wires in the board. The devices are connected to the board in a variety of methods. One method is soldering a ball grid array (BGA) package to conductive pads on the board.
However, this current method has its disadvantages. For example, the PWB may not be planar. The BGA's are manufactured to tight tolerances so that a solid connection to the board is ensured. In addition, for high pin count devices, the pitch, or distance, between the pins will be on the order of millimeters. Therefore, if the PWB is not planar, the BGA attachment may not have a complete connection to the board. Initially, the weak connection may cause intermittent communication failure with the other devices on the PWB. Over time this connection may become completely disconnected rendering the device unusable.
Another example is the effect of warpage. Most of today's PWBs are built in multiple layers comprised of a variety of materials. These materials have different coefficients of thermal expansion. When exposed to the specified temperatures of the system (e.g., −40 degrees Celsius to 140 degrees Celsius), the different layers of the board expand and contract at different rates, thus causing warpage of the board. Over time, the board will become non-planar and the rigid connection of the BGA and solder to the PWB will be unable to accommodate the warpage of the PWB resulting in disconnects between the BGA and the PWB.
In the above situations, a field engineer may remove the board and try to replace the part that is disconnected. There is risk in damaging the board when removing the BGA. There is also risk in reducing the life of the device or permanently disabling the device when reattaching the BGA balls and reattaching the BGA to the board. Also, there are many applications where replacement of parts is not possible thus creating a need to have a more robust connection of a BGA to a board.